The present invention relates to a system for separating and removing foreign particles from an airstream supplied to the intake passage of an aircraft engine. More particularly, it relates to an actuating linkage system for use with an engine provided with an air intake duct having a double door type of particle separator, anti-icing system installed therein.
Aircraft engines require a flow of atmospheric air for their operation. The engine inlet and air intake ducting direct the required flow of air to the engine air intake provided at the entrance face of the compressor. Variations in the pressure of this incoming flow of air generally decrease the efficiency of the engine. More particularly, decreases in the pressure of the airflow reaching the engine air intake result in successively magnified power losses through the other engine components. Such decreases in the pressure generally arise because aircraft engines are required to operate in a variety of weather conditions and from variously prepared landing sites. Debris in the atmosphere as, for example, sand, stones, birds and the like, may pose a serious hazard if ingested by the engine, because they tend to block the air intake or may cause extensive damage to or erosion of the compressor blades. Operation of the aircraft in snow, hale, mixed icing, and other weather conditions commonly results in the accumulation of ice or slush on the air intake of the engine which decreases the incoming airflow to the compressor. The latter may lead to serious losses of power and may in the extreme case lead to engine burnout.
Various protective devices and methods have been employed to remove the aforementioned foreign particles from the incoming airstream of aircraft engines. One method particularly applicable to engines having centrally located air intakes, for example, a gas turbine propeller aircraft engine, is to provide an air intake duct which is arranged to extend parallel to the engine and has an inertial particle separator installed therein, as is described in U.S. Pat. No. 3,329,377. Generally, an air intake duct is elongated and has a forward facing open inlet at one end, a discharge outlet at the other end, and an intermediate side opening disposed in the side wall of the engine. The inertial particle separator is provided in the form of a fixed deflecting vane which is placed within the duct between the forward facing inlet and the side opening in the engine side wall. The deflecting vane is installed at a fixed angle within the interior of the air intake duct such that the internal cross-section of the duct is gradually reduced. Incoming air is deflected through a substantial angle around the trailing edge of the deflecting vane and up into the side opening leading to the engine, while ice and other particles having greater inertia pass in a substantially unimpeded path through the duct and thence out the discharge outlet to the atmosphere. The inertial particle separator thus divides the incoming air flow into two parts, with one stream of clean air being directed towards the engine air intake and the other stream carrying ice and other debris being ducted overboard. The inertial particle separator is an effective means of preventing foreign particles from entering the engine air intake. At the same time, however, it does decrease the pressure of the incoming airflow reaching the engine air intake by dividing the incoming airflow. There are certain flight modes of operation when the full power provided by full ram effect of the incoming airflow is necessary, as for example, during rapid ascent, take-offs and high speed maneuvering of the craft. The above mentioned prior art system does not have the capability of providing such full ram effect of the incoming air and hence is limited for use with certain aircraft.
In another prior art inertial particle separator anti-icing system the air intake duct is provided with an adjustable deflecting vane and in addition, an adjustable bypass door disposed at the downstream portion of the duct. In this prior art air intake system, the deflecting vane may be raised to a stowed position out of the path of the incoming airflow while the bypass door may be raised to block off the discharge outlet such that all of the incoming airflow is directed through the side opening leading to the engine air intake. The relative positions of the deflecting vane and the bypass door in the latter case correspond to the air intake system in the ram mode position. The latter system may be alternately shifted to an anti-icing mode in which the deflecting vane is lowered into the path of the incoming airflow to act as an inertial particle separator, while the bypass door is lowered to a stowed position so as to open the discharge outlet. At normal air speeds, the incoming airflow exerts relatively large aerodynamic forces on the deflecting vane and the bypass door, so that individual boost actuators are provided to assist in varying the positions of the bypass door and the deflecting vane. The dual door anti-icing system affords an air intake system which may be shifted between a ram mode position and an anti-icing mode position as required for operation of the engine. However, individual actuators for both the deflecting vane and the bypass door generally have a high failure rate. Thus, for example, in the worst case, if the actuator for the bypass door fails while the bypass door is in its stowed position, and the actuator for the deflecting vane fails while the deflecting vane is in its stowed position, incoming air flows through the duct and out of the discharge outlet without being directed to the engine air intake. The latter causes an almost complete loss of power in the engine. Alternatively, the actuator for the bypass door may fail with the bypass door in its stowed position while the actuator for the deflecting vane remains operative so that the aircraft can only be operated at the decreased power provided when the air intake system is in the anti-icing mode. Since the actuators are usually electromechanical, the pilot may not become aware of a system failure until a large decrease in power is felt, and even then, the pilot does not known at first which part of the system has failed and what actions need to be taken. Since the failure rate of actuators is generally high, it has been found that pilots have lost confidence in the prior art anti-icing system whereby pilots operate the aircraft in ram mode only, for fear of not being able to restore the system to ram mode after shifting to anti-icing mode. Of course, in so doing, the pilots are inviting all of the attendant dangers associated with not removing ice and other particles from the incoming airflow to the engine.
Accordingly, in order to overcome the shortcomings of the prior art devices, it is an object of the subject invention to provide an anti-icing system which is effective in preventing the ingress of water, snow, ice and other debris into the air intake of an aircraft engine.
It is another object of the subject invention to provide an anti-icing system which may be shifted alternately between a ram mode position and an anti-icing mode position with reliability.
It is a further object of the subject invention to provide a manually operative anti-icing system which is directly under the pilot's control, so that the pilot is assured at all times that the system is operative.
It is still another object of the subject invention to provide an anti-icing system which is designed to be fail-safe, such that the failure of the system components does not invalidate the system function or the ensuing flight safety of the aircraft.